Drum-type inkjet printing systems generally include one or more fixed inkjet print heads (also called pens) positioned circumferentially around a rotating cylindrical drum. The print media (e.g. paper) is carried by the rotating drum past the print heads, which eject drops of ink in a desired pattern upon the print media.
In order to maintain good image quality, proper maintenance of the pen-to-pen alignment and pen-to-paper spacing is desirable. However, if the print drum translates or wobbles on its bearings as it rotates, the accuracy of inkjet drop placement on the print media can be adversely affected. Wobbling or runout of a rotating print drum can occur in several ways, and the various types of drum wobbling can affect both pen-to-pen alignment and pen-to-paper spacing in the printer, and thereby adversely affect print quality, such as by producing banding and/or grain in the printed image.